Coxsackievirus

A 4-year-old boy is brought to the emergency department by his parent because of difficulty in feeding him for a day. The parent reports that the patient felt warm last night, but he did not have any chills, myalgia, cough or sneezing. Past medical history is unremarkable. The patient is up to date on his vaccinations. Temperature is 37.7°C (100°F), pulse is 80/min, respirations are 19/min and blood pressure is 110/78 mmHg.  Physical examination shows a maculopapular and vesicular rash scattered on the palms and soles bilaterally. Oropharyngeal examination shows superficial ulcers with a greyish-yellow base and an erythematous rim on the tongue and buccal mucosa. Which of the following is the most likely causative agent of this patient’s condition?